The principal objective of this proposal is to study the mechanisms involved in the control of transcription and translation of retrovirus genes during the cell cycle of the host. Synchronized cultures of virus infected cells (i.e. mouse, chicken), obtained by an automated procedure for the selective detachment of mitotic cells, will be used to study the following aspects of viral gene expression during the cell cycle: a) pattern of viral RNA synthesis in uninfected and infected cells (i.e. endogenous and chronically infected viral RNA). The relative rate of viral RNA synthesis will be determined from the amount of nuclear RNA, pulse labeled at different times of the cell cycle, that hybridizes to excess viral complementary DNA. The total amount of viral RNA in synchronized cells will be calculated from the rate of hybridization of labeled viral cDNA probes to excess cellular RNA; b) pattern of viral protein synthesis and its relation to transcription. This will be obtained from the amount of pulse labeled cellular protein corresponding to viral protein as judged by immunoprecipitation and electrophoretic procedures; c) processing of viral precursor proteins. Electrophoretic separation of viral proteins; labeled at various times of the cell cycle, chased and immunoprecipitated, will give us this information; d) pattern of expression of viral antigens on the cell surface. This will be studied in vitro labeling of cell surface antigens with 125I, at particular phases of the cell cycle, followed by immunoprecipitation and fractionation of the viral antigens; e) pattern of virus release and its relation to transcription and translation of viral genes.